1. Field of the Invention
The present invention relates to a drive apparatus for a zoom lens barrel.
2. Description of the Related Art
A zoom lens is generally composed of at least two movable zooming lens groups which are moved in predetermined directions upon zooming. In a classic drive mechanism therefor, the movable zooming lens groups are moved along tracks defined by cam grooves formed on a cam ring so as not to cause the focal shift. This drive mechanism has been widely used in a single lens reflex camera in which no focal shift during zooming is permitted. Alternatively, in a drive mechanism used for a compact camera or digital camera in which the lens must be precisely focused upon shutter releasing, the zooming lens groups are moved while permitting the focal shift during zooming, and the zooming lens groups are moved to the in-focus position upon shutter releasing, in accordance with set focal length data and object distance data. In the drive mechanism for the compact camera or digital camera, two separate drive units are provided for the two movable zooming lens groups wherein the positions of the zooming lens groups is detected and represented by digital data. The "zooming" referred to in this specification includes two modes, i.e., the first mode in which the zooming lens groups are moved so as not to cause the focal shift and the second mode in which the zooming lens groups are moved permitting the focal shift. As a matter of course, it is possible to move the movable zooming lens groups so as not to cause the focal shift in the drive mechanism for the second mode.
The second type of drive mechanism for a zoom lens barrel in which the drive unit is provided for each of the two movable zooming lens groups is larger and more complex than the first type of drive mechanism in which the two movable zooming lens groups are moved by a single cam ring.